The invention relates to a belt retractor for an occupant restraint system.
In addition to the usual belt webbing and/or vehicle-sensitive locking functions modern belt retractors are equipped with additional functions where necessary. One of these additional functions is safeguarding loads or child seats by a state of blockage which is activated by complete unwinding and subsequent retraction of the belt webbing. Switching back into the locking condition in case of an emergency is achieved by complete retraction of the belt webbing. Another additional function is a belt fastening detection for which the withdrawn belt webbing length is determined.
Such additional functions of a belt retractor necessitate a high complexity of mechanical components. Particularly complex is to provide different types of belt retractors for the respective additional functions requested.
This is achieved in a belt retractor for an occupant restraint system comprising a frame, a belt reel rotatably mounted in the frame, an electric motor drive coupled to the belt reel, a locking mechanism for selectively blocking the belt reel, and a vehicle-sensitive sensor. The locking mechanism is actuated by an actuator. An electronic control unit is provided with an input interface and an output interface. The vehicle-sensitive sensor is connected to the input interface, and the actuator and the electric motor drive are connected to the output interface.
The invention provides a novel belt retractor having a uniform mechanical basic design enabling a series of additional functions to be achieved when requested.
Instead of the conventional retraction spring the belt retractor according to the invention provides an electric motor instead of the conventional retraction spring which loads the belt reel with the retraction torque required in each case. The functions of the belt retractor are controlled by an electronic control unit including an input interface and an output interface. The vehicle-sensitive sensor is connected to the input interface and the actuator is connected to the output interface, as is the electric motor. This basic concept facilitates the adaption of the locking and retraction functions of the belt retractor to the respective requirements, since merely program data need to be adapted, according to which the electronic control unit works. Furthermore, various sensors can be connected to the input interface of the electronic control unit, the output signals of which are taken into account in driving the locking mechanism. Likewise further actuators or positioners and the like may be connected to the output interface of the electronic control unit, the functions of which are controlled in dependence of the sensor signals as polled via the input interface of the electronic control unit. The control unit signals the electric motor to provide a belt tensioning when the signal constellation of a plurality of sensors, connected to the input interface indicates an imminent vehicle collision. The control unit takes into account at least one of the following sensor signals: ABS signal, braking pressure signal, acceleration signal, vehicle speed signal, engine speed signal, belt force signal and absolute belt reel angle of rotation.
In the preferred embodiment the belt retractor includes an electric motor, more particularly a servo motor, which not only carries out the task of the retraction spring in a conventional mechanical belt retractor but also can ensure a pretension of the belt webbing in an imminent vehicle crash.
One of the sensors connected to the input interface yields in the preferred embodiment an incremental signal representing the rotation of the belt reel, preferably in conjunction with a further signal indicating the sense of rotation. These signals are analyzed by the electronic control unit by up/down counting to determine the absolute angle of rotation of the belt reel and thus the length of the belt webbing withdrawn.
In this preferred embodiment of the belt retractor has the following functions, some of which may also be achieved only when required:
child seat/load safeguarding
belt fastening detection
vehicle-sensitive blocking: where the belt reel of the belt retractor is blocked when a vehicle-sensitive sensor signals a severe vehicle impact;
retraction spring;
comfort gearing: smooth gear transmission between the motor shaft and the belt reel;
blocking on non-locked seatback: where the belt reel is blocked when the backrest of a vehicle seat is not a locked position (to indicate that the backrest should be locked before the seat belt is fastened);
belt webbing-sensitive blocking: where the belt reel is blocked when the belt webbing is abruptly pulled;
belt webbing pretensioning.
On the basis of a uniform electromechanical basic concept, numerous embodiments, differing in terms of functionality, can be provided with the belt retractor system according to the invention. The functionality is essentially determined by the sensors connected to the input interface of the electronic control unit and by the unerasably stored program according to which the control unit operates.
The preferred embodiment provides additional functions which can not be realized in conventional belt retractors. One of these additional functions is the precautionary tensioning of the belt webbing in a critical situation, e.g. a full braking. By making use of a high-performance electric motor drive a tensioning force of 250 N or more is possible. A tensioning travel of 120 mm or more for a tensioning time of only about 120 ms is realistic. Such pretensioning enables the belt slack to be eliminated already prior to an accident to minimize the risk of injury of the vehicle occupants and to optimize the effectiveness of the conventional belt tensioner, in particular the pyrotechnic-type belt tensioner.
Belt webbing pretensioning may also be used to correct the sitting posture of a vehicle occupant to minimize the risk of injury by inflatable restraint means (air bag).
When, following a belt webbing pretensioning, normal driving conditions reoccur, belt tensioning can be reversed.
On the other hand, after pretensioning of the belt webbing and subsequent release have occurred, a renewed pretensioning of the belt webbing is possible.
In the preferred embodiment the electric motor is coupled by a toothed belt to a gearwheel side-mounted to the belt reel, the gearwheel having a diameter larger than that of the drive pinion of the electric motor. The toothed belt is set under tension by a belt tightener as a function of the load. In normal operation the belt tension is small, so that the drive works extremely silent and with low wear. On tensioning of the belt webbing, the belt tension is increased in order to assure a transmission of force without skipping of teeth. At the same time, there is achieved an optimum balance in terms of tooth clearance and tolerances.
The electric motor employed is preferably a low-wear, brushless four-phase motor, its bifilar stator winding achieving low commutating losses. Using a motor with an outside rotor a compact design is achieved. The outside rotor carries preferably a 14-pole neodymium magnetic ring to enable a high drive moment in line with a compact design, particularly in a short-time overload operation. Two Hall sensors yield the rotor position, the sense of rotation and, from this, the length of belt webbing withdrawn.
The locking mechanism of the belt retractor consists of an apertured disk on the flange of the belt reel and a latching pin mounted axially shiftable and spring-loaded at the frame of the retractor, that pin being selectively latched in the holes of the apertured disk of the belt reel. This engagement of the latching pin in the holes of the apertured disk is facilitated by lead-in ramps adjacent to the holes. The latching pin is maintained in the non-activated resting position by an electromagnet. In the non-energized condition the latching pin is moved into the locked position by the spring loading.
The electronic control unit of the belt retractor meets more particularly the following requirements:
motor commutation;
torque control;
overload protection:
drive of the belt reel release;
control of all comfort and safety functions;
continual computation of the actual belt withdrawal length via the absolute angle of rotation of the belt reel;
input signals of the various connected sensors, discretely and via a connected bus system (CAN):
fast 8-bit control unit with idle mode and integrated EEPROM;
stator integrated on printed circuit board.
In the preferred embodiment of a vehicle occupant restraint system all belt retractors have the same electro-mechanical basic design and differ only in their functionality determined substantially by the program data stored in the electronic control unit. Thus, for example, the functionality of the front belt retractors differ from those of the rear belt retractors. The electronic control units of all belt retractors may be linked to a common central sensor.